1. Field of the Invention
The present invention relates to an automated high efficiency chemical processor that permits the purification or reprocessing of chemicals contaminated with water and other materials.
2. Background of the Invention
Numerous technologies use or supply chemicals in their manufacturing process. The price for chemicals increases dramatically as the purity requirement increases. Transportation of chemicals from remote sites to the manufacturing facility can reduce chemical purity through the generation of undesired micron and sub-micron sized particles. Transportation of chemicals can likewise expose the general population to hazardous substances. The environmental impact of disposing of large quantities of spent or contaminated chemicals is becoming socially unacceptable and adding excessive cost to the manufacturing cycle. Manufacturers are looking for ways to purify and/or re-use ultra-pure chemicals directly at their manufacturing locations.
This is particularly true in the manufacturing processes of electronic and semiconductor devices. There, parts, such as integrated circuit wafers and printed circuit boards, must be washed in concentrated acid in either an etching step or a cleaning step. One specific example is the pre-diffusion cleaning and photoresist stripping that is accomplished in the manufacture of integrated circuit wafers through the use of concentrated sulfuric acid and accompanying oxidants, for instance, an aqueous solution of hydrogen peroxide.
Inevitably, therefore, the acid baths used for the above purposes become contaminated, such as from the materials cleaned or etched, mixed; or become mixed with the water carried by the oxidant, and/or absorb water from various sources. In addition to water, the acids typically contain particulate impurities, cations, anions, and organic compounds. Although some contaminants, such as certain particulates, may be removed by filtering or other simple purification techniques, it has been difficult to completely regenerate the concentrated acid. In particular, because acids are in general hydrophilic, it has heretofore been difficult to remove sufficient water.
Consequently, there has been a tendency for industries to generate large quantities of acid wastes. This is neither economical nor environmentally sound. Thus, a need exists for small scale, on-site equipment for reprocessing of such chemicals. Also, some manufacturers have a need to initially purify lower grade chemicals to ultra-pure grade. Indeed, the art has recognized this need and there has been increased attention to the development of methods and apparatus to recycle and purify chemical wastes, such as acids. E.g., U.S. Pat. Nos. 4,828,660 and 4,855,023.
In these aforementioned patents, the oxidizing agents and other contaminants were first stripped from the used contaminated acids, with the combination of heating the mixture and purging the mixture with air or an inert gas stream to remove the water. However, this process is a continuous process, and no endpoint detection or reflux control was provided. Nevertheless, a interesting finding was that the resulting recycled concentrated acids may, in some cases, be more pure than the commercially purchased starting acid.
In U.S. Pat. Nos. 5,225,048 and 5,236,555, a method and an apparatus are disclosed, respectively, to concentrate liquids through a distillation process utilizing constant, predetermined parameters. Such parameters include, water content and flow rate of the feed, the distillate flow rate, and the heating power for the distillation column. These copending applications are directed primarily at situations in which the chemical sought to be purified is more volatile than water. More specifically, they are directed toward reprocessing single or multiple-phase organic solvents that are more volatile than water.
In co-pending U.S. patent application Ser. No. 08/002,995, a method and an apparatus are disclosed for the continuous or semi-continuous purification of chemical compounds that are less volatile than their contaminants. The purified product is removed from the bottom of the column, i.e., from the distillation pot after driving off the less volatile contaminants. The method uses predetermined operating conditions.
In the case of concentrated acids, and also many other chemical compounds, the chemical compound sought to be purified is less volatile than water. In such situations, many problems not encountered with more volatile chemicals will become evident to one skilled in the art.
Sulfuric acid reprocessing is typically accomplished in the industry through use of continuous or continuous batch processing systems.
In such systems, at least two (and often three) columns are needed to carry out the reprocessing process. In such processes, larger quantities of equipment and complex operating conditions are necessary. Those factors combine to increase the cost of the systems. In addition, the systems are relatively complicated to operate, require a significant amount of plant space, numerous external connections, and produce purified product in such quantities that only large scale users realize the full benefit of the equipment.
Accordingly, there is a need in the art for a low cost, compact, fully automated purification and/or reprocessing system that is able to function with high efficiency and deliver ultra-pure chemical without the need for engineers or technicians to continually operate and monitor the system.